Back light

ABSTRACT

A backlight unit includes a light source having an emission region, a wiring board having the light source mounted thereon, a light guide plate having a side surface into which light from the light source enters, and a front surface from which the light exits, a light shielding adhesive tape adhering to the wiring board, and an optical sheet which overlaps with the front surface of the light guide plate. The front surface of the light guide plate includes an effective region serving as a planar light source and a light entering region ranging from the side surface to the effective region. The wiring board and the light-shielding adhesive tape each have a part positioned in the light entering region, and the optical sheet is arranged from the effective region to the light entering region. An end portion of the optical sheet overlaps with the light-shielding tape.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 13/572,757, filed Aug. 13, 2012, the contents of which areincorporated herein by reference.

The present application claims priority from Japanese application JP2011-177436 filed on Aug. 15, 2011, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a display device.

2. Description of the Related Art

In a display device including a side-light type backlight unit, lightentering an end surface of a light guide plate travels inside the lightguide plate and exits from a front surface of the light guide plate(Japanese Patent Application Laid-open No. 2009-276531). As a lightsource of the backlight unit, a light emitting diode (LED) is generallyused. The LED is mounted on a flexible wiring board and is arranged soas to face the end surface of the light guide plate. Further, an opticalsheet is arranged on the front surface of the light guide plate.

When the flexible wiring board is fixed to an end portion of the frontsurface of the light guide plate with a light-shielding double-sidedtape, on the front surface side of the light guide plate, there isformed a gap from which the light guide plate is exposed between thelight-shielding double-sided tape and the optical sheet. Light exitingfrom the gap does not pass through the optical sheet and enters adisplay panel from an end surface thereof. Therefore, when the displaypanel is obliquely viewed, the light of the LED may be directlyobserved, which causes a problem of display quality degradation.

SUMMARY OF THE INVENTION

The present invention has an object to provide a display device which iscapable of blocking leakage light from a light guide plate to preventquality degradation.

(1) According to an exemplary embodiment of the present invention, thereis provided a display device, including: a display panel; and abacklight unit to be used as a planar light source of the display panel.The backlight unit includes: a light source having an emission regionnarrower than an emission region of the planar light source; a wiringboard having the light source mounted thereon; a light guide platehaving an end surface into which light from the light source enters, anda front surface from which the light exits; a light-shieldingpressure-sensitive adhesive sheet for causing the wiring board to adhereto an end portion of the front surface of the light guide plate; and alight diffusion sheet which overlaps with the front surface of the lightguide plate. The front surface of the light guide plate includes aneffective region serving as the planar light source and a light enteringregion ranging from the end surface into which the light enters to theeffective region. The wiring board and the light-shieldingpressure-sensitive adhesive sheet each have a part positioned in thelight entering region. The light diffusion sheet is arranged from theeffective region to the light entering region, and at least an endportion thereof overlaps with the light-shielding pressure-sensitiveadhesive sheet in the light entering region. On a side closer to theeffective region with respect to the light-shielding pressure-sensitiveadhesive sheet, the light entering region is covered with the lightdiffusion sheet without a gap. According to the exemplary embodiment ofthe present invention, the light diffusion sheet and the light-shieldingpressure-sensitive adhesive sheet are provided in an overlapping mannerwithout a gap. Therefore, the leakage light from the light guide platecan be blocked to prevent quality degradation.

(2) In the display device as described in Item (1), at least a part ofthe light-shielding pressure-sensitive adhesive sheet may be interposedbetween the wiring board and the light guide plate.

(3) In the display device as described in Item (1), the light-shieldingpressure-sensitive adhesive sheet may adhere from a surface of thewiring board directed to a side opposite to the light guide plate to thefront surface of the light guide plate.

(4) In the display device as described in Item (2) or (3), thelight-shielding pressure-sensitive adhesive sheet may include anoverlapping portion with the wiring board, the light-shieldingpressure-sensitive adhesive sheet extending off from the overlappingportion in a direction of the effective region, and overlapping with thelight diffusion sheet outside the wiring board.

(5) In the display device as described in Item (4), the light-shieldingpressure-sensitive adhesive sheet may overlap with the light diffusionsheet arranged on the light guide plate.

(6) In the display device as described in Item (4), the light diffusionsheet may overlap with the light-shielding pressure-sensitive adhesivesheet arranged on the light guide plate.

(7) In the display device as described in any one of Items (4) to (6),the light diffusion sheet may include a non-overlapping portion at whichoverlapping with the light-shielding pressure-sensitive adhesive sheetis avoided, and the display device may further include a light-shieldingfilm which is formed so as to cross a boundary between the overlappingportion and the non-overlapping portion.

(8) In the display device as described in Item (2), the light diffusionsheet may be arranged so as to reach a surface of the wiring boarddirected on a side opposite to the light guide plate, and the lightdiffusion sheet may overlap with the light-shielding pressure-sensitiveadhesive sheet through an intermediation of the wiring board.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a sectional view illustrating a display device according to anembodiment to which the present invention is applied;

FIG. 2 is a sectional view illustrating a display device according to afirst modified example of the embodiment;

FIG. 3 is a sectional view illustrating a display device according to asecond modified example of the embodiment;

FIG. 4 is a sectional view illustrating a display device according to athird modified example of the embodiment; and

FIG. 5 is a sectional view illustrating a display device according to afourth modified example of the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention is described withreference to the drawings.

FIG. 1 is a sectional view illustrating a display device according to anembodiment to which the present invention is applied. The display deviceincludes a display panel 10. The display panel 10 is a light-shuttertype display panel which controls passing and blocking of light todisplay an image. The display panel 10 illustrated in FIG. 1 is a liquidcrystal display panel, and includes a pair of substrates 12 and 14 madeof glass and the like, liquid crystal (not shown) sandwiched between thesubstrates, and polarizing plates 18 arranged on outer sides of the pairof substrates 12 and 14, respectively.

One substrate (lower substrate in FIG. 1) 12 extends off from anothersubstrate (upper substrate in FIG. 1) 14. On a surface of the onesubstrate 12 on a side opposed to the another substrate 14 in a partwhich extends off from the another substrate 14, there is mounted anintegrated circuit chip 20 having a driver circuit embedded therein, fordriving the liquid crystal. Further, a flexible wiring board 22 is fixedto the part on which the integrated circuit chip 20 is mounted.

The display device includes a backlight unit 24 which is used as aplanar light source of the display panel 10. The backlight unit 24includes a light source 26. The light source 26 is a point light sourcesuch as a light emitting diode (LED). The point light source has anarrower emission region than that of the planar light source. The lightsource 26 emits white light.

The light source 26 is mounted on a wiring board 28 such as a flexibleprinted circuit (FPC) board, and is electrically connected to a wiringpattern (not shown) on the wiring board 28. The wiring board 28 isarranged so that the light source 26 is directed downward (to a sideopposite to the display panel 10). The wiring board 28 includes a partwhich overlaps with the light source 26 and a part outside a region onwhich the light source 26 is mounted. The wiring board 28 is arranged soas to overlap with at least an end portion of the display panel 10.Further, the wiring board 28 is arranged so as to overlap with theintegrated circuit chip 20. The wiring board 28 is opaque, but does nothave a light-shielding property and transmits light.

The backlight unit 24 includes a light guide plate 30. The light guideplate 30 is provided for converting the light of the light source 26(point light source) into a planar light source to illuminate thedisplay panel 10 with the planar light source. The light from the lightsource 26 enters an end surface of the light guide plate 30. For theentrance of the light from the light source 26, the end portion of thelight guide plate 30 is arranged adjacent to the light source 26. Thewiring board 28 is positioned on the light source 26, and an end portionof the wiring board 28 overlaps with the light guide plate 30. The lightsource 26 and the light guide plate 30 may be provided in contact witheach other, or a gap may be provided therebetween. Light exits in aplanar shape from a front surface 32 of the light guide plate 30. Thefront surface 32 of the light guide plate 30, which performs planaremission, is opposed to the display panel 10. The front surface 32 ofthe light guide plate 30 includes an effective region 34 as the planarlight source, and a light entering region 36 ranging from the endsurface, into which light enters, to the effective region 34.

The backlight unit 24 includes a light diffusion sheet 38 which overlapswith the front surface 32 of the light guide plate 30. The lightdiffusion sheet 38 is arranged on the light guide plate 30 (on a sidecloser to the display panel 10). The light diffusion sheet 38 isarranged in a range from the effective region 34 to the light enteringregion 36 of the light guide plate 30. The light diffusion sheet 38 hasa weak light diffusion action, and hence influence on light distributioncan be weakened when light passes through the light diffusion sheet 38.On the light diffusion sheet 38 (on a side closer to the display panel10), a plurality of prism sheets 40 are arranged. When light passesthrough the prism sheets 40, light is collected to the front side toincrease the front brightness. The light diffusion sheet 38 and theprism sheets 40 are collectively called an optical sheet. Further, belowthe light guide plate 30 (on a side opposite to the display panel 10), areflective sheet 42 is arranged.

The display device includes an inner frame 44, and the backlight unit 24is arranged inside the inner frame 44. The inner frame 44 is a resinmolded product, and is also called a mold. The inner frame 44 supportsthe display panel 10. The display panel 10 is adhered to the inner frame44 by a double-sided tape 46. In the example illustrated in FIG. 1, alower surface of a left end portion of the double-sided tape 46 isadhered to the inner frame 44, and an upper surface of a right endportion of the double-sided tape 46 is adhered to the polarizing plate18 of the display panel 10. The double-sided tape 46 has alight-shielding property. The double-sided tape 46 covers the wiringboard 28 having the light source 26 mounted thereon, and extends offfrom the wiring board 28. Therefore, with the double-sided tape 46,light emitted from the light source 26 to pass through the wiring board28 and light leaked from a periphery of the wiring board 28 are blocked.Note that, the double-sided tape 46 is also adhered to the wiring board28 and the prism sheet 40.

The inner frame 44 surrounds and holds the light guide plate 30 and thelight source 26. The wiring board 28 having the light source 26 mountedthereon is adhered to the inner frame 44 with a double-sided tape 48.Specifically, the wiring board 28 extends in mutual opposite directionsfrom the region on which the light source 26 is mounted, and one endportion thereof is adhered to the inner frame 44 in an overlappedmanner. The double-sided tape 48 is interposed between the wiring board28 and the inner frame 44. The double-sided tape 48 has alight-shielding property. The inner frame 44, the backlight unit 24, andthe display panel 10 are housed in an outer frame 50.

The backlight unit 24 includes a light-shielding pressure-sensitiveadhesive sheet 52. The light-shielding pressure-sensitive adhesive sheet52 includes a light-shielding layer and a pressure-sensitive adhesivelayer (both not shown). When the light-shielding layer is black, thelight-shielding layer can absorb light to reduce light reflection. Thepressure-sensitive adhesive layer is formed on both surfaces of thelight-shielding layer. When the pressure-sensitive adhesive layer is aninsulating member, the light-shielding layer may be a conductor.Further, the double-sided tape 48 and the light-shieldingpressure-sensitive adhesive sheet 52 may be integrated with each other.

The light-shielding pressure-sensitive adhesive sheet 52 causes thewiring board 28 to adhere to an end portion of the front surface 32 ofthe light guide plate 30. The wiring board 28 and the light-shieldingpressure-sensitive adhesive sheet 52 each have a part positioned in thelight entering region 36 of the light guide plate 30. At least a part ofthe light-shielding pressure-sensitive adhesive sheet 52 is interposedbetween the wiring board 28 and the light guide plate 30. Thelight-shielding pressure-sensitive adhesive sheet 52 includes anoverlapping portion with respect to the wiring board 28, and extends offfrom the overlapping portion in a direction of the effective region 34.In the light entering region 36 of the light guide plate 30, thelight-shielding pressure-sensitive adhesive sheet 52 overlaps with thelight diffusion sheet 38 outside the wiring board 28. In the lightentering region 36, at least an end portion of the light diffusion sheet38 overlaps with the light-shielding pressure-sensitive adhesive sheet52. On a side closer to the effective region 34 with respect to thelight-shielding pressure-sensitive adhesive sheet 52, the light enteringregion 36 is covered with the light diffusion sheet 38 without a gap.The light diffusion sheet 38 overlaps with the light-shieldingpressure-sensitive adhesive sheet 52 arranged on the light guide plate30.

According to this embodiment, the light diffusion sheet 38 overlaps withthe light-shielding pressure-sensitive adhesive sheet 52 without a gap,and hence it is possible to block the leakage light from the light guideplate 30 to prevent quality degradation.

FIG. 2 is a sectional view illustrating a display device according to afirst modified example of the embodiment. In this example, the lightdiffusion sheet 38 includes an overlapping portion with thelight-shielding pressure-sensitive adhesive sheet 52, and anon-overlapping portion at which the overlapping is avoided. On thelight diffusion sheet 38, a light-shielding film 54 is formed so as tocross a boundary between the overlapping portion and the non-overlappingportion. The light-shielding film 54 may be formed by printing and thelike. With the light-shielding film 54, it is possible to prevent lightleakage from the boundary between the overlapping portion and thenon-overlapping portion. Other configurations correspond to the contentsdescribed in the above-mentioned embodiment.

FIG. 3 is a sectional view illustrating a display device according to asecond modified example of the embodiment. In this example, thepositions of the light diffusion sheet 38 and the light-shieldingpressure-sensitive adhesive sheet 52 are inverted from those of theexample of FIG. 1. That is, the light-shielding pressure-sensitiveadhesive sheet 52 overlaps with the light diffusion sheet 38 arranged onthe light guide plate 30. Other configurations correspond to thecontents described in the above-mentioned embodiment.

FIG. 4 is a sectional view illustrating a display device according to athird modified example of the embodiment. In this example, a lightdiffusion sheet 138 is arranged so as to reach a surface of the wiringboard 28 which is directed to a side opposite to the light guide plate30. Specifically, the light diffusion sheet 138 extends from theeffective region 34 to the light entering region 36 of the light guideplate 30 to run on the wiring board 28.

The light diffusion sheet 138 overlaps with a light-shieldingpressure-sensitive adhesive sheet 152 through an intermediation of thewiring board 28. The light-shielding pressure-sensitive adhesive sheet152 adheres to the wiring board 28 and the light guide plate 30. Thelight-shielding pressure-sensitive adhesive sheet 152 is arranged onlyat a position at which the wiring board 28 overlaps with the light guideplate 30, and does not directly adhere to the light diffusion sheet 138.

A double-sided tape 146 which causes the display panel 10 to adhere tothe inner frame 44 is positioned on the light diffusion sheet 138 on thewiring board 28. As is understood through comparison to the example ofFIG. 1, in the example of FIG. 4, the light diffusion sheet 138 servesas a spacer so that the double-sided tape 146 adheres to the displaypanel 10 even on the wiring board 28. A surface of the double-sided tape146 on a side opposite to the display panel 10 adheres to the lightdiffusion sheet 138. That is, the double-sided tape 146 causes thedisplay panel 10 and the light diffusion sheet 138 to adhere to eachother. Other configurations correspond to the contents described in theabove-mentioned embodiment.

FIG. 5 is a sectional view illustrating a display device according to afourth modified example of the embodiment. In this example, alight-shielding pressure-sensitive adhesive sheet 252 adheres from thesurface of the wiring board 28 directed to a side opposite to the lightguide plate 30 to the front surface 32 of the light guide plate 30.Further, the light-shielding pressure-sensitive adhesive sheet 252covers the upper side of the light source 26, and hence has an effect ofblocking light passing through the wiring board 28.

A double-sided tape 246 which causes the display panel 10 to adhere tothe inner frame 44 is positioned on the light-shieldingpressure-sensitive adhesive sheet 252 on the wiring board 28. Thelight-shielding pressure-sensitive adhesive sheet 252 serves as a spacerso that the double-sided tape 246 adheres to the display panel 10. Asurface of the double-sided tape 246 on a side opposite to the displaypanel 10 adheres to the wiring board 28 and the light-shieldingpressure-sensitive adhesive sheet 252. Other configurations correspondto the contents described in the above-mentioned embodiment. Note that,for the overlapping of the light-shielding pressure-sensitive adhesivesheet 252 with the light diffusion sheet 38. the light-shieldingpressure-sensitive adhesive sheet 252 may be positioned above the lightdiffusion sheet 38, or the light diffusion sheet 38 may be positionedabove the light-shielding pressure-sensitive adhesive sheet 252.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A backlight comprising: a light emitting diode; awiring board; a light guide plate; an optical sheet; and a double-sidedtape, wherein the light emitting diode has an emission region and ismounted on the wiring board, the light guide plate has a side surfaceinto which light from the light emitting diode enters and a frontsurface from which the light exits, the optical sheet overlaps with thefront surface of the light guide plate, the double-sided tape adheres tothe wiring board, the front surface of the light guide plate includes aneffective region serving as a planar light source and a light enteringregion between the side surface and the effective region, and theoptical sheet overlaps with the double-sided tape in the light enteringregion.
 2. The backlight according to claim 1, wherein the double-sidedtape overlaps with the light emitting diode.
 3. The backlight accordingto claim 1, wherein the double-sided tape adheres to the optical sheet.4. The backlight according to claim 1, wherein the double-sided tape isfor adhering to a display panel.
 5. The backlight according to claim 1,wherein the double-sided tape has a light shielding layer.
 6. Abacklight comprising: a light emitting diode having an emission region;a wiring board having the light emitting diode mounted thereon; a lightguide plate having a side surface into which light from the lightemitting diode enters and a front surface from which the light exits; anadhesive tape adhered to the wiring board; and an optical sheet disposedabove the front surface of the light guide plate, wherein the frontsurface of the light guide plate comprises an effective region foroutputting the light from the light emitting diode and a light enteringregion provided between the effective region and the side surface,wherein the optical sheet extends from the effective region to the lightentering region and overlaps with the adhesive tape in the lightentering region.
 7. The backlight according to claim 6, wherein theadhesive tape overlaps with the light emitting diode.
 8. The backlightaccording to claim 6, wherein the adhesive tape adheres to the opticalsheet.
 9. The backlight according to claim 6, wherein the adhesive tapeis for adhering to a display panel.
 10. The backlight according to claim6, wherein the adhesive tape has a light-shielding layer.